Work vehicles such as lift trucks, automated guided vehicles, mobile transporters and the like are often utilized for transferring a load such as, a pallet, a work piece, a tub and the like between load transfer stations such as, storage areas, machining cells, conveyors and assembly lines. These load transfer stations have often have propelled devices such as, motor driven conveyors, drills, mills, grinders etc. which require a source of electric energy. Thus, the facility is fixedly wired in an appropriate manner to transfer electrical current from the house main to the electric drive motors. This permanent wiring is satisfactory in applications where the work being performed remains constant over a relatively long period of time. However, in applications where the load transfer stations are frequently moved due to changes in storage, machining and assembly requirements, the fixed wiring is a problem. Often the ability to move the wiring is extremely difficult due to the construction of the facility and very costly in both time and money.
In applications where there are numerous load transfer stations the cost and complexity associated with providing electrical wiring for each station is substantial. As a result of this excessive cost the number of load transfer stations is reduced from the optimum. As a result the efficiency of the operation is less than achievable which ultimately increases the cost of the product or service to the customer.
Each of the load transfer stations, in addition to requiring electrical energy for powering the motors, require communication sensors for the purpose of turning on and off the motors when a load is ready to be transferred from the work vehicle. It is emphasized that each load transfer station requires communication sensors. As a result the cost and complexity of each load transfer station is increased.
It has been known to drive a load transfer station conveyor by a vehicle mounted mechanical drive system of the friction or coupling type. One such a system is shown in European Patent No. 0100867, to Max Braendli et al, which published on Feb. 22, 1984. This patent discloses an automatic guided vehicle having a roller deck and a conveyor stand having a roller deck. A coupling half on the vehicle is matable with a coupling half on the conveyor at an aligned position of the coupling half. The coupling half on the vehicle is connected to a roller deck drive motor and transfers powered rotary motion from the conveyor drive motor through the coupling half to the coupling half on the conveyor stand. The conveyor stand coupling half is drivingly connected to the conveyor stand rollers and rotates the rollers in response to rotation thereof. A mechanical drive system such as this is not satisfactory in that the amount of power being transferred and the speed of operation is limited to the functional characteristics of the vehicle conveyor drive motor. Thus, the maximum size of the conveyor stand is limited in load capacity, conveyor length and the like. As a result, the number of applications are limited to just a few.
In addition to the size limitation of the stand mounted conveyor, the two coupling halves must be accurately aligned relative to each other in order to permit successful mating and power transfer. Thus, the surface upon which the vehicle operates must be of the highest quality in order to maintain accuracy in the distance from the surface to each of the coupling halves. In applications where a large number of conveyor stands are used the cost of providing such close tolerances is extremely difficult. The dynamics of the vehicle further adds to the alignment problems. Since the load being carried on the vehicle will vary in magnitude the elevational distance between the surface and the coupling will also vary. This is based factors such as vehicle frame deflection, tire crush and suspension sag.
In the event that the automatic guided vehicle docks at a skewed or angled position relative to the conveyor the ability to successfully achieve coupling will be unlikely. This will result in undesirable down time and delays until the problem is corrected such as, by manual intervention by a vehicle system operator.
In automatic guided vehicles in which mechanical power transfer, such as disclosed in the Max Braendli et al. publication, is provided, extreme accuracy of docking is mandatory. In order to achieve this accuracy a sophisticated vehicle control system is required. Such a system utilizes expensive and elaborate sensors to identify when the vehicle is in position to dock. Such systems often fail to be accurate enough to precisely locate the vehicle relative to the conveyor stand. Thus, premature wear of the mechanical drive coupling or failure to mate often occurs.
Mechanical drives such as shown in the Max Braendli et al. publication do not transfer of electrical energy for the powering of secondary functions on the load transfer station. Therefore, control of the conveyor, the load being transferred, the stop gates on the load transfer station and the like is not available. As a result the controllability and flexibility of operation of the load transfer station is limited and only mechanical conveyor drive is provided.
The present invention is directed to overcoming one or more of the problems as set forth above.